1. Field of the Invention
The invention relates generally to detecting radiation levels in brachytherapy and, more particularly, to an apparatus and method for detecting, measuring and altering dosage levels in brachytherapy treatments.
2. Related Art
Brachytherapy has become a common treatment for cancer but is used less often in other applications. In brachytherapy, radioactive “seeds” or sources are placed in or near tumors or other types of diseased tissues. As a result, low radiation dose (LDR) or high radiation dose (HDR) is given to the tumor while reducing the radiation exposure in the surrounding healthy tissues. The term “brachy” is Greek for short distance, and brachytherapy is radiation therapy given at a short distance: localized and precise. Brachytherapy may be used for a wide range of diseases, including, for example, soft tissue sarcoma, head and neck tumors, breast cancer, prostate cancer, intravascular plaques or similar conditions.
Using prostate cancer as an example, there are currently two types of brachytherapy suitable for treating prostate cancer: permanent seed implantation, which is typically LDR, and temporary brachytherapy, which may be HDR. Permanent seed implant procedures typically include injecting radioactive seeds into and/or around the prostate gland. The therapeutic seeds give off radiation, at a low dose rate over several weeks or months, and then the seeds remain in and/or around the prostate gland permanently.
Temporary brachytherapy instead involves inserting tiny plastic catheters (perhaps several) into and/or around the prostate gland, and then giving a series of radiation treatments through these catheters. The catheters are then easily pulled out with no radioactive material left behind. Typically, a computer-controlled machine called an afterloader pushes a single radioactive seed, such as an iridium-192 seed, into each of the catheter(s) and controls the exposure duration. The computer can also control the exposure in different parts of the prostate such by varying exposure times in different catheters. Moreover, individual control over each catheter can selectively regulate exposure so that a high dosage is given to the tumor while ensuring a reduced dosage to neighboring tissue, such as the rectum or urethra. The ability to modify the dose after insertion of the catheters is one advantage of temporary brachytherapy over permanent seed implants.
Currently, high intensity radiation sources used in HDR brachytherapy are quite accurately measured for total activity, but the geometric distribution of radiation is assumed to be uniform. But, clinical results from recently developed techniques, such as intravascular brachytherapy, indicate that this assumption may not be accurate, resulting in the under or over exposure of tissues and compromising the quality of the therapy. In addition, there is currently no method for measuring the real-time multi-dimensional tissue dose distribution. Instead, tissue density mapping may be obtained from magnetic resonance imaging and x-ray computed tomography. These tissue density maps show catheter positions and are often utilized in combination with the total source dose, and nominal source positions and dwell times from the afterloader device, in Monte Carlo simulations to calculate the dose distribution in tissue. However, relying on simulations does not provide any actual measured dose distribution and therefore any over or under exposure is typically determined post therapy by the physiological response. Without ability to measure actual dosage distribution during brachytherapy, adjustments of the dose distribution cannot be made during treatments so that a more desired effect can be achieved such as assuring more effective targeting of tumors, or avoiding irradiation of nearby healthy tissue.
Accordingly, there is a need to be able to characterize a radiation source to aid in creating a brachytherapy treatment plan based on the characterized radiation source. Furthermore, there is a need to a have a way to measure actual radiation dosages delivered in brachytherapy when using the characterized radiation source to determine tissue dosimetry so that a way of altering the treatment plan, based on the actual measurements, might be achieved. In this way, a desired dosage level and distribution of radiation might be more accurately delivered during the course of treatment.